Update hackney to fix sslv3 reference on OTP 23

This fixes the following error when using OTP 23:

```
 ** (Protocol.UndefinedError) protocol String.Chars not implemented for {:options, {:sslv3, {:versions, [:"tlsv1.2", :
        (elixir 1.10.3) lib/string/chars.ex:3: String.Chars.impl_for!/1
        (elixir 1.10.3) lib/string/chars.ex:22: String.Chars.to_string/1
        lib/excoveralls/poster.ex:58: ExCoveralls.Poster.send_file/2
        lib/excoveralls/poster.ex:13: ExCoveralls.Poster.execute/2
        (mix 1.10.3) lib/mix/tasks/test.ex:484: Mix.Tasks.Test.do_run/3
        (mix 1.10.3) lib/mix/task.ex:330: Mix.Task.run_task/3
        lib/mix/tasks.ex:54: Mix.Tasks.Coveralls.do_run/2
        (mix 1.10.3) lib/mix/task.ex:330: Mix.Task.run_task/3
        (mix 1.10.3) lib/mix/cli.ex:82: Mix.CLI.run_task/2
        (elixir 1.10.3) lib/code.ex:926: Code.require_file/2
```

The error is due to hackney previously adding sslv3 to the ssl_options
when they aren't specified and OTP 23 removing support for sslv3.
Hackney 1.16.0 fixes this.

mix.exs

@@ -36,7 +36,7 @@ defmodule ExCoveralls.Mixfile do
       {:mock, "~> 0.2", only: :test},
       {:meck, "~> 0.8", only: :test},
       {:jason, "~> 1.0"},
-      {:hackney, "~> 1.0"},
+      {:hackney, "~> 1.16"},
       {:ex_doc, "~> 0.21.0", only: :dev}
     ]
   end

mix.lock

@@ -1,18 +1,18 @@
 %{
-  "certifi": {:hex, :certifi, "2.3.1", "d0f424232390bf47d82da8478022301c561cf6445b5b5fb6a84d49a9e76d2639", [:rebar3], [{:parse_trans, "3.2.0", [hex: :parse_trans, optional: false]}]},
-  "earmark": {:hex, :earmark, "1.4.3", "364ca2e9710f6bff494117dbbd53880d84bebb692dafc3a78eb50aa3183f2bfd", [:mix], [], "hexpm"},
-  "ex_doc": {:hex, :ex_doc, "0.21.2", "caca5bc28ed7b3bdc0b662f8afe2bee1eedb5c3cf7b322feeeb7c6ebbde089d6", [:mix], [{:earmark, "~> 1.3.3 or ~> 1.4", [hex: :earmark, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.14", [hex: :makeup_elixir, repo: "hexpm", optional: false]}], "hexpm"},
-  "hackney": {:hex, :hackney, "1.13.0", "24edc8cd2b28e1c652593833862435c80661834f6c9344e84b6a2255e7aeef03", [:rebar3], [{:certifi, "2.3.1", [hex: :certifi, optional: false]}, {:idna, "5.1.2", [hex: :idna, optional: false]}, {:metrics, "1.0.1", [hex: :metrics, optional: false]}, {:mimerl, "1.0.2", [hex: :mimerl, optional: false]}, {:ssl_verify_fun, "1.1.1", [hex: :ssl_verify_fun, optional: false]}]},
-  "idna": {:hex, :idna, "5.1.2", "e21cb58a09f0228a9e0b95eaa1217f1bcfc31a1aaa6e1fdf2f53a33f7dbd9494", [:rebar3], [{:unicode_util_compat, "0.3.1", [hex: :unicode_util_compat, optional: false]}]},
-  "jason": {:hex, :jason, "1.1.1", "d3ccb840dfb06f2f90a6d335b536dd074db748b3e7f5b11ab61d239506585eb2", [:mix], [{:decimal, "~> 1.0", [hex: :decimal, optional: true]}]},
-  "makeup": {:hex, :makeup, "1.0.0", "671df94cf5a594b739ce03b0d0316aa64312cee2574b6a44becb83cd90fb05dc", [:mix], [{:nimble_parsec, "~> 0.5.0", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm"},
-  "makeup_elixir": {:hex, :makeup_elixir, "0.14.0", "cf8b7c66ad1cff4c14679698d532f0b5d45a3968ffbcbfd590339cb57742f1ae", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}], "hexpm"},
-  "meck": {:hex, :meck, "0.8.13", "ffedb39f99b0b99703b8601c6f17c7f76313ee12de6b646e671e3188401f7866", [:rebar3], [], "hexpm"},
-  "metrics": {:hex, :metrics, "1.0.1", "25f094dea2cda98213cecc3aeff09e940299d950904393b2a29d191c346a8486", [:rebar3], []},
-  "mimerl": {:hex, :mimerl, "1.0.2", "993f9b0e084083405ed8252b99460c4f0563e41729ab42d9074fd5e52439be88", [:rebar3], []},
-  "mock": {:hex, :mock, "0.3.2", "e98e998fd76c191c7e1a9557c8617912c53df3d4a6132f561eb762b699ef59fa", [:mix], [{:meck, "~> 0.8.8", [hex: :meck, optional: false]}]},
-  "nimble_parsec": {:hex, :nimble_parsec, "0.5.3", "def21c10a9ed70ce22754fdeea0810dafd53c2db3219a0cd54cf5526377af1c6", [:mix], [], "hexpm"},
-  "parse_trans": {:hex, :parse_trans, "3.2.0", "2adfa4daf80c14dc36f522cf190eb5c4ee3e28008fc6394397c16f62a26258c2", [:rebar3], []},
-  "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.1", "28a4d65b7f59893bc2c7de786dec1e1555bd742d336043fe644ae956c3497fbe", [:make, :rebar], []},
-  "unicode_util_compat": {:hex, :unicode_util_compat, "0.3.1", "a1f612a7b512638634a603c8f401892afbf99b8ce93a45041f8aaca99cadb85e", [:rebar3], []},
+  "certifi": {:hex, :certifi, "2.5.2", "b7cfeae9d2ed395695dd8201c57a2d019c0c43ecaf8b8bcb9320b40d6662f340", [:rebar3], [{:parse_trans, "~>3.3", [hex: :parse_trans, repo: "hexpm", optional: false]}], "hexpm", "3b3b5f36493004ac3455966991eaf6e768ce9884693d9968055aeeeb1e575040"},
+  "earmark": {:hex, :earmark, "1.4.3", "364ca2e9710f6bff494117dbbd53880d84bebb692dafc3a78eb50aa3183f2bfd", [:mix], [], "hexpm", "8cf8a291ebf1c7b9539e3cddb19e9cef066c2441b1640f13c34c1d3cfc825fec"},
+  "ex_doc": {:hex, :ex_doc, "0.21.2", "caca5bc28ed7b3bdc0b662f8afe2bee1eedb5c3cf7b322feeeb7c6ebbde089d6", [:mix], [{:earmark, "~> 1.3.3 or ~> 1.4", [hex: :earmark, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.14", [hex: :makeup_elixir, repo: "hexpm", optional: false]}], "hexpm", "f1155337ae17ff7a1255217b4c1ceefcd1860b7ceb1a1874031e7a861b052e39"},
+  "hackney": {:hex, :hackney, "1.16.0", "5096ac8e823e3a441477b2d187e30dd3fff1a82991a806b2003845ce72ce2d84", [:rebar3], [{:certifi, "2.5.2", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "6.0.1", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "1.0.1", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~>1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:parse_trans, "3.3.0", [hex: :parse_trans, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "1.1.6", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}], "hexpm", "3bf0bebbd5d3092a3543b783bf065165fa5d3ad4b899b836810e513064134e18"},
+  "idna": {:hex, :idna, "6.0.1", "1d038fb2e7668ce41fbf681d2c45902e52b3cb9e9c77b55334353b222c2ee50c", [:rebar3], [{:unicode_util_compat, "0.5.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "a02c8a1c4fd601215bb0b0324c8a6986749f807ce35f25449ec9e69758708122"},
+  "jason": {:hex, :jason, "1.1.1", "d3ccb840dfb06f2f90a6d335b536dd074db748b3e7f5b11ab61d239506585eb2", [:mix], [{:decimal, "~> 1.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "639645cfac325e34938167b272bae0791fea3a34cf32c29525abf1d323ed4c18"},
+  "makeup": {:hex, :makeup, "1.0.0", "671df94cf5a594b739ce03b0d0316aa64312cee2574b6a44becb83cd90fb05dc", [:mix], [{:nimble_parsec, "~> 0.5.0", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "a10c6eb62cca416019663129699769f0c2ccf39428b3bb3c0cb38c718a0c186d"},
+  "makeup_elixir": {:hex, :makeup_elixir, "0.14.0", "cf8b7c66ad1cff4c14679698d532f0b5d45a3968ffbcbfd590339cb57742f1ae", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}], "hexpm", "d4b316c7222a85bbaa2fd7c6e90e37e953257ad196dc229505137c5e505e9eff"},
+  "meck": {:hex, :meck, "0.8.13", "ffedb39f99b0b99703b8601c6f17c7f76313ee12de6b646e671e3188401f7866", [:rebar3], [], "hexpm", "d34f013c156db51ad57cc556891b9720e6a1c1df5fe2e15af999c84d6cebeb1a"},
+  "metrics": {:hex, :metrics, "1.0.1", "25f094dea2cda98213cecc3aeff09e940299d950904393b2a29d191c346a8486", [:rebar3], [], "hexpm", "69b09adddc4f74a40716ae54d140f93beb0fb8978d8636eaded0c31b6f099f16"},
+  "mimerl": {:hex, :mimerl, "1.2.0", "67e2d3f571088d5cfd3e550c383094b47159f3eee8ffa08e64106cdf5e981be3", [:rebar3], [], "hexpm", "f278585650aa581986264638ebf698f8bb19df297f66ad91b18910dfc6e19323"},
+  "mock": {:hex, :mock, "0.3.2", "e98e998fd76c191c7e1a9557c8617912c53df3d4a6132f561eb762b699ef59fa", [:mix], [{:meck, "~> 0.8.8", [hex: :meck, repo: "hexpm", optional: false]}], "hexpm", "1d63e81180518c413647e97ad141beeb9b75046715731ed3fca58c0232a4201d"},
+  "nimble_parsec": {:hex, :nimble_parsec, "0.5.3", "def21c10a9ed70ce22754fdeea0810dafd53c2db3219a0cd54cf5526377af1c6", [:mix], [], "hexpm", "589b5af56f4afca65217a1f3eb3fee7e79b09c40c742fddc1c312b3ac0b3399f"},
+  "parse_trans": {:hex, :parse_trans, "3.3.0", "09765507a3c7590a784615cfd421d101aec25098d50b89d7aa1d66646bc571c1", [:rebar3], [], "hexpm", "17ef63abde837ad30680ea7f857dd9e7ced9476cdd7b0394432af4bfc241b960"},
+  "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.6", "cf344f5692c82d2cd7554f5ec8fd961548d4fd09e7d22f5b62482e5aeaebd4b0", [:make, :mix, :rebar3], [], "hexpm", "bdb0d2471f453c88ff3908e7686f86f9be327d065cc1ec16fa4540197ea04680"},
+  "unicode_util_compat": {:hex, :unicode_util_compat, "0.5.0", "8516502659002cec19e244ebd90d312183064be95025a319a6c7e89f4bccd65b", [:rebar3], [], "hexpm", "d48d002e15f5cc105a696cf2f1bbb3fc72b4b770a184d8420c8db20da2674b38"},
 }